We studied the effects of experimentally induced emotions on inhibitory control using functional magnetic resonance tomography (fMRI). The Simon task used involves two conditions with different attentional demands and is a well established paradigm for studying inhibitory control. Incompatible trials demand cognitive control for resolving interference. Compatible trials need no inhibitory control. Twelve participants viewed a series of affective pictures inducing positive, negative or neutral affects. Between the picture blocks, participants performed either incompatible or compatible trials. Behavioral and fMRI data revealed an impact of negative emotions only on the processing of ncompatible trials. Subjects made more errors and showed less activation of brain areas associated with task performance. There was no effect of positive emotions neither on compatible nor incompatible trials. The results first showed that especially the processing of negative emotions is resource competing and secondly that the competition concerns only the controlled route of cognitive processing.